Manual]Physics actions: Global settings
These actions affect Physics behaviors in general, not just the one it was set for.
By default, all Physics objects collide with each other. You can disable collisions between the object and another Physics object so they pass through each other. This affects all instances of both object types. Note: enabling collisions again when objects are overlapping can cause instability in the simulation.
Perhaps in conjunction with setting the objects with physics to immovable it could be close enough to enabling/disabling ?
IIRC, there was an example of switching between physics and platform behavior that was quite a while ago and is listed in the how do I FAQ (link in my signature).